Make C++11 mandatory now. Also from this point forward, the version number bump will occur after the release

CHANGELOG

@@ -1,3 +1,5 @@
+0.82.7 (next)
+  - C++11 is now mandatory to compile DOSBox-X
 0.82.6
   - Resizing the window in SDL 1.x Windows builds
     fixed to work correctly in the latest build

configure.ac

@@ -1,5 +1,5 @@
 dnl Init.
-AC_INIT(dosbox-x,0.82.6,[https://github.com/joncampbell123/dosbox-x/issues],[],[http://dosbox-x.software])
+AC_INIT(dosbox-x,0.82.7,[https://github.com/joncampbell123/dosbox-x/issues],[],[http://dosbox-x.software])
 AC_PREREQ(2.60)
 AC_CONFIG_SRCDIR(README)
 
@@ -131,9 +131,7 @@ AC_CHECK_CXXFLAGS([ -std=gnu++11 ], [  ], [
 ])
 
 if test x$warn_cpp0x = x1; then
-    AC_MSG_ERROR([ C++0x is considered deprecated. Please use a C++11 compiler.
-C++0x support will be removed at a future date entirely.
-To disable this error, remove or comment out line 133-137 of configure.ac, run autogen.sh and try again. ])
+    AC_MSG_ERROR([ Your compiler must support C++11 or better ])
 fi
 
 dnl This is how the build script can specify a HX DOS extender target